Identification of strain rate-dependent mechanical behaviour of DP600 under in-plane biaxial loadings

The rate-dependent hardening behaviour of dual phase DP600 steel sheet is investigated by means of in-plane biaxial tensile tests, in an intermediate strain rate range (up to 20 s−1) and for large strains (up to 30% of equivalent plastic strain) at room temperature. The dynamic biaxial in-plane tensile tests are performed on a dedicated cruciform specimen shape previously developed and validated for large strains at quasi-static conditions. To perform dynamic biaxial tensile tests, a specific device is used to reduce oscillations on measure of forces. Based on these experiments, parameters of two phenomenological strain-rate hardening models (saturated and power law), are identified. Material parameters are obtained from an optimisation process, based on the finite element modelling of the biaxial test, by minimising differences between experimental and simulated principal strains at the specimen centre. A comparison of the strain hardening functions calibrated from both biaxial and uniaxial tensile tests under static and dynamic conditions are then proposed. Results show that the biaxial procedure developed in this work, associated with a specific shape of the cross specimen, are more efficient to determine the rate-dependent hardening behaviour for large strains than the conventional uniaxial tensile test.